A new fluoriemtric ultramicromethod was developed for quantiative determination of cyclic 3',5'-AMP as derivative of dansyl chloride using silica gel thin-layer chromatography. In presence of dansyl chloride cyclic 3',5'-AMP formed a fluorescent complex. A spot of dansyl derivative of cyclic 3',5'-AMP was photographed on a reversible colour film, after which the colour intensity of the spot on the film was determined directly by a special densitometer. Content of cyclic 3',5'-AMP was studied in different regions of rat brain. The in fluence of some psychotropic drugs on the level of cyclic 3',5'-AMP was studied using this method. The method was highly sensitive and reproducible and enabled to determine 10(-10) -- 10(-11) M cyclic 3',5'-AMP.